This invention relates to handling of workpieces so that a continuous throughput is achieved for processing in a vacuum environment.
A great variety of manufacturing processes require a vacuum environment. For example, sputtering, plasma etching, evaporation and chemical vapor deposition are common processes in the fabrication of semiconductor devices and all require a vacuum. In order to be cost effective, such processes could include some means for continuous throughput of the workpieces into and out of the vacuum chamber. This usually requires advancing the workpieces through a series of pumping stations of succesively reduced pressure until the workpieces enter the vacuum chamber and then successively increasing pressure from the vacuum chamber to the environment.
Continuous throughput, therefore, usually requires some type of sealing mechanism which prevents leaks between pumping stations as the workpieces move through. Providing such a mechanism involves considerable difficulty, however, since the seal must typically be able to withstand, without substantial leaks, a large pressure drop if employed adjacent to the entrance from or exit to the atmosphere. The mechanism must also provide as little friction as possible so as not to impede the movement of the workpieces. This is a particular problem where the workpieces are large, such as the panels from which printed circuit boards are formed, which typically measure 61.0 cm.times.45.7 cm.times.1.57 mm.